FujiFilm S2800HD has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Canon A800 has a
10.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features DIGIC 3 processor.
Below you can see the S2800HD and A800 sensor size comparison.
FujiFilm S2800HD and Canon A800 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.